In a UX context, I've heard the Facebook Like Button described as a "platform primitive". Is this accurate, and can anyone expand on the meaning of platform primitive in this context?
When talking about graphics, the term "geometric primitive" typically means …
the simplest (i.e. 'atomic' or irreducible) geometric objects that the system can handle (draw, store).
With regards to a platform's design system, then, a "platform primitive" is the simplest UI/design element than cannot be reduced further. You would not be able to use such an element (at least within the context of its platform) if you'd remove any elements from it.
In other words, remove the label and/or icon from the (platform-primitive!) "button" widget, and you'd be left with a plain rectangle. ;)
It's just another way of saying that, in the context of the platform, that element is an "atom" in Brad Frost's "Atomic Design" concept.
I believe it's simply stating that it (the like button) is primitive to the platform (Facebook). Primitive means:
relating to, denoting, or preserving the character of an early stage in the evolutionary or historical development of something.
having a quality or style that offers an extremely basic level of comfort, convenience, or efficiency.
In that context, I believe they mean that the like button is a core (and early) feature of Facebook.